Coatings are applied to a wide variety of substrates for widely divergent purposes. Just a few examples of the many different types of coatings include adhesive coatings, primer coatings, decorative coatings, protective hard coatings, varnish coatings, antireflective coatings, reflective coatings, interference coatings, release coatings, dielectric coatings, photoresist coatings, conductive coatings, nonlinear optic coatings, electrochromic/electroluminescent coatings, barrier coatings, biologically-active coatings, biologically inert coatings, and the like. Such coatings can be applied to substrates that are made from many different materials and have many different shapes. For example, in terms of materials, substrates can be metal, wood, cloth, polymeric, ceramic, paper, mineral, glass, composite, and the like. In terms of shape, substrates can be flat, curved, undulating, twisted, microstructured, smooth, rough, porous, particulate, fibrous, hollow shaped, three-dimensional, regular or irregular surfaced, and the like.
In conventional industrial coating processes, an admixture (which can be an emulsion, solution, slurry, two-phase fluid mixture, and the like) comprising the coating constituents and a suitable solvent is applied to the substrate using a suitable coating technique such as spraying, roll coating, brush coating, spin coating, or the like. The coated composition then is typically dried and cured in order to solidify the coating. During drying, the solvent is removed from the coating and then discarded into the environment or recovered.
The solvent is generally an essential component of the coating composition for a variety of reasons. First, the solvent helps ensure that the coating composition has a suitable coating viscosity. The solvent also helps ensure that the coating composition can be applied to the substrate evenly to form a uniform coating. The solvent may also provide the composition with an acceptable shelf-life.
The presence of the solvent, however, has many drawbacks. If the solvent is to be discarded after use, the solvent becomes waste in the environment. This is particularly problematic if the solvent is hazardous. Indeed, disposal of hazardous solvents tends to involve expensive and elaborate disposal schemes regulated by governmental authorities in an effort to minimize harm to the environment resulting from the disposal. Solvent recovery, therefore, is often preferred to solvent disposal. However, solvent recovery, like solvent disposal, also suffers from several disadvantages. Firstly, solvent recovery tends to require expensive, capital intensive procedures and equipment. Sometimes, the materials used to clean a solvent are hazardous wastes themselves.
In short, the need to handle the solvents from coating operations is a serious burden in industry. Accordingly, it would be desirable to find a way to carry out coating operations with minimal solvent, or more preferably, in solventless fashion, to avoid the burden of having to dispose of, or recover, left-over solvent. It would also be desirable to find a way to accomplish this for a wide variety of different coating compositions.